The present invention pertains generally to high tear strength, high tensile strength paper products. More particularly, this invention relates to high tear strength, high tensile strength paper products useful as a substitute for woven products such as cotton cloth of the same basis weight.
Woven products are very versatile materials. One of the reasons for their wide versatility is that they possess not only a high tensile strength, but also a high tear strength. Cotton cloth for example, is currently used in place of paper in many applications, such as backings for abrasive materials, because paper does not possess the requisite combination of tear and tensile strength.
There have been various attempts to increase generally the strength of paper materials. One of these methods is the preparation of paper and non-woven fabric from synthetic fibers disclosed in U.S. Pat. No. 3,200,033. Specifically, the object of the invention is to provide a method where a latex adhesive is added only in an amount necessary for bonding the crossing points of the non-woven fiber. The preferred latex adhesive is a polyurethane forming mixture of polyesters and polyisocyanates whose isocyanate groups are blocked by an alcohol or phenol and become reactive only at a temperature of about 100.degree. C.
Another method of increasing the strength of paper products is found in Pontius U.S. Pat. No. 4,504,290. Pontius relates to a sheet material comprising a combination of cellulose and synthetic fiber in a weight percentage range from between at least 30 to 50% of cellulose fibers and 1 to 10% of synthetic fibers.
Brandon et al U.S. Pat. No. 4,512,849 demonstrates that in some instances, in order to increase the initial wet web strength, hydrated (fibrillated) wood or other natural fibers and/or fibrillated, synthetic fibers have been combined with non-fibrillated, synthetic fiber finishes. Such combinations have tended to hold non-woven webs together while they have been transferred from a moving, forming wire across unsupported draws, to wet presses or other treating equipment, where a binder has been added to hold the fibers together more permanently. However, the use of the fibrillated, natural or synthetic fibers as part of the finish has not proven satisfactory for non-wovens intended for use as replacement fabrics for textiles. This has been because of the stiff, "papery" hand imparted by these fibrillated fibers to the resulting non-wove fabrics. The solution of Brandon et al, is a composition of at least 50% by weight of staple length, synthetic, hydrophobic fibers having a length to diameter ratio of about 1000:3000 and a length of at least 1/2 inch.
U.S. Pat. No. 4,865,691 discloses a method for internally strengthening products from fibrous materials characterized by the use of a wet-end additive. The wet-end addition is a particular grade of polyvinyl alcohol which is super-hydrolyzed and which is substantially insoluble in water maintained at 130.degree. F.
The problem with the aforementioned processes, however, is that they achieve only an increased tear or tensile strength but not the requisite combination of a high tear strength and high tensile strength that would be necessary to replace woven fabrics of the same basis weight. For this reason, woven fabrics such as cotton cloth continue to be used in numerous applications as opposed to paper because, as was mentioned, they possess a superior combination of tear and tensile strength compared to paper products of the same basis weight.
Accordingly, it is an object of the present invention to provide a high tear strength, high tensile strength paper product.
It is another object of the present invention to provide a high tear strength, high tensile strength paper product with a tear strength and tensile strength at least equal to that of cotton cloth of the same basis weight.
It is yet another object of the present invention to provide a high tear strength, high tensile strength paper product which is of lower cost to produce than is a cotton cloth of the same basis weight possessing similar tear and tensile strength.
Still another object of the present invention is to provide a paper product that has a tear and tensile strength at least equal to that of cotton cloth of the same basis weight which is also less permeable than cotton cloth and possesses a final surface that is smoother than that of cotton cloth.
These and other objects of the present will become apparent to the skilled artisan upon a review of the following specification and the claims appended thereto.